SLOVYANSK, Ukraine — Ukraine's Interior Ministry says 4 officers have been killed and 30 wounded in gunbattles with pro-Russia militants occupying the eastern city of Slovyansk.

Slovyansk has been the heart of an uprising in east Ukraine against the central government in Kiev, which came to power after the country's Russia-leaning president fled following months of street protests.

A statement on the ministry's website on Monday did not give further details about how those officers died. But a separate statement said Ukrainian troops had started an "anti-terrorist operation" Monday morning against the pro-Russia forces, which numbered around 800.

THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.

Ukrainian troops fought pitched gunbattles Monday with a pro-Russia militia occupying an eastern city, and the government sent an elite national guard unit to re-establish control in the southern port city of Odessa.

The twin moves reflected an apparent escalation of efforts to bring the region back under Kiev's control.

Associated Press reporters heard gunfire and multiple explosions in and around Slovyansk, a city of 125,000 people that has become the focus of the armed insurgency against the new interim government in Kiev.

Interior Minister Arsen Avakov said on his agency's website that pro-Russia forces were deploying large-caliber weapons and mortars in the region and there were injured on both sides. Government troops were facing about 800 insurgents, he said.

A pro-Russia militia spokesman in Slovyansk said an unspecified number of people had been killed and wounded in the clashes, including a 20-year-old woman killed by a stray bullet.

Both sides indicated fighting was taking place at several sites around the city. An Associated Press crew saw at least four ambulances rushing injured people to a city hospital, and one militiaman was seen being carried in for medical treatment.

Ukraine is facing its worst crisis in decades as the polarized nation of 46 million tries to decide whether to look toward Europe, as its western regions want to do, or improve ties with Russia, which is favored by the many Russian-speakers in the east.

The goals of the pro-Russian insurgency are ostensibly geared toward pushing for broader powers of autonomy for the region, but some insurgents do favor separatism.

In the last few weeks, anti-government forces have stormed and seized government buildings and police stations in a dozen eastern Ukrainian cities. Authorities in Kiev — who blame Russia for backing the insurgents — have up to now been largely powerless to react. And since Russia has kept tens of thousands of troops along Ukraine's eastern border — and annexed its key Black Sea peninsula of Crimea last month — Ukraine's central government fears Russia could try to invade and grab more territory.

Kiev also moved Monday to restore control over the Black Sea port city of Odessa, where pro-Russian activists vowed on Monday to take over government buildings.

Odessa had remained largely peaceful even as violence erupted across east Ukraine until 46 people died Friday after riots broke out between pro-Russian and pro-Ukrainian groups and a government building was set on fire.

Pro-Russian activists gathered Monday at the funeral of a regional member of parliament, Vyacheslav Markin, who was known for speaking out against the government in Kiev. They shouted "Hero! Hero!" and vowed to avenge his death.

"Kiev doesn't control the situation in the country, Kiev controls only one half of Ukraine," said 32-year-old Dmitry Sheiko, who was wearing the St. George black-and-orange ribbon, a ubiquitous symbol of the pro-Russia protest movement. "Even in Odessa they can't maintain order, which means that we will restore order ourselves."

The weekend riots have also brought into question the loyalty of Odessa's police forces. On Sunday, pro-Russian demonstrators stormed the Odessa police headquarters and freed 67 people who had detained in the rioting.

The Interior Ministry said in a statement Monday that it was sending an elite national guard unit from Kiev to re-establish control in the city, and said 42 of those arrested during the rioting were being sent to another region for investigation, presumably to prevent local police from releasing more prisoners.

Russia, which the international community has accused of promoting the unrest, has vociferously condemned Ukraine's recent security operations in the east.